Daddy long legs spiders are not poisonous or harmful to dogs. While they do have venom, it is very mild and their fangs are generally too small to deliver venom effectively to mammals, including dogs. If a dog eats a daddy long legs, it is very unlikely to cause any adverse reactions or poisoning. These spiders are considered harmless to pets and humans alike, and the myth that daddy long legs are highly venomous is unfounded scientifically.